A skid-steer loader, skid loader, or skidsteer, is a type of small hydraulic vehicle with a generally rigid frame having lift arms used to attach a variety of labor-saving tools or attachments, and is typically powered with an on-board engine. Skid-steer loaders are typically four-wheel vehicles with the wheels mechanically locked in synchronization on each side and locked in driving orientation to the vehicle (i.e., they do not turn left or right). The left-side drive wheels can be driven independently of the right-side drive wheels. The machine turns by skidding, or dragging its fixed-orientation wheels across the ground. Skid-steer loaders are capable of zero-radius turns, making them extremely maneuverable and valuable for applications that require a compact, agile loader. Skid-steer loaders are sometimes equipped with tracks in lieu of the wheels and such a vehicle is known as a “compact track loader.” Unlike in a conventional front loader, the lift arms in these machines are alongside the driver with the pivot points behind the driver's shoulders.
The hydrostatic drive mechanism for driving the wheels may be interconnected with the hydraulic system controlling the lift and tilt cylinders of the boom assembly of the skid-steer vehicle.
A valve assembly is a hydraulic device that controls hydraulic fluid from a hydraulic pump to different movable members in hydraulic systems such as construction and industrial equipment. Each movable member is controlled by a hydraulic section that consists of a body with a pair of work ports, and a pump inlet and tank outlet. A control spool inside the body controls the flow of fluid to and from the different ports. An assembly can consist of a single section to operate a single movable member or a plurality of sections to operate a plurality of movable members. If multiple movable members are involved, one of the methods of controlling the flow of fluid is an industry accepted hydraulic circuit identified as a series circuit. The series circuit allows the different movable members to be connected to each other by way of the valve assembly. This connection offers an advantage of recycling return flow from moving members that are activated to downstream moving members.